Prior art engines have been designed that have a pair of eccentric control shafts for adjusting engine compression ratio. These engines have a piston slidably mounted in a working cylinder, a crankshaft mounted in a crankcase, and a connecting rod for connecting the piston to the crankshaft. The working cylinder is formed in a cylinder jug that is movable relative to the crankcase for adjusting the compression ratio of the engine. The eccentric control shafts form two expand expandable hinge pin joints. Bushings in the crankcase form a first half of the hinged joint, and bushings in the cylinder jug form the second half of the hinged joint. The control shafts are a form of hinge pins and have off-set journal bearings. Rotating the two control shafts in unison adjusts the position of the cylinder jug relative to the crankshaft and thereby adjusts the compression ratio of the engine. The control shafts are typically located on opposite sides of the engine and parallel to the crankshaft to provide stable support of the cylinder jug in the crankcase.
The prior art engine designs having a pair of eccentric control shafts typically employ removable bearing caps located on the crankcase for assembly of the eccentric control shaft in the engine. A problem with these engines is that they would be expensive to manufacture and expensive to assemble due to the large number of bearing caps that need to be bolted together. A second problem is low mechanical stiffness and strength. The problem of low strength and stiffness is compounded in engines where the parting line of the bearing cap is oriented vertically, rather than horizontally for best supporting the high mechanical forces encountered in internal combustion engines. A number of prior art designs have eccentric control shaft bearings that are not mechanically functional because the bearings are too small. Another problem with these engines is size and weight. Regarding size, a large distance or bridging distance between the eccentric control shafts can results in excessive bending of the crankcase when it is under load. A large bridging distance can also result in excessive thermal expansion distortion between the crankcase and cylinder jug. A narrow engine is also needed for fitting the engine in existing engine bays, and a light weight engine is needed for minimizing vehicle fuel consumption. The crankcase must also be sealed for containing engine oil inside of the crankcase. A number of prior art designs do not teach how to enclose the crankcase. Specifically, these prior art engine designs do not teach how to assemble the control shafts in the crankcase without removable bearing caps or by other means, or how to provide the necessary crankcase sealing.
A variable compression ratio engines having dual eccentric control shafts is taught by Eichi Kamiyama shows in U.S. Pat. No. 7,806,092, and Akihisa et al. in U.S. Pat. No. 7,047,917. Eichi Kamiyama shows a variable compression ratio engine having an eccentric hinge pin assembly 25c, 25c1, 25c2, 25c3 and 25c4 retained in crankcase bearing caps 25a, 25a2 and jug bearing caps or bearing blocks 25b. Crankcase bearing caps 25a2 are bolted to crankcase 21, and jug bearing caps or bearing blocks 25b are bolted to jug 23. Both the crankcase and the cylinder jug have removable bearing caps. A problem with the invention taught in U.S. Pat. Nos. 7,806,092 and 7,047,917 is that it is expensive to manufacture and expensive to assemble due to the large number of bearing caps that need to be bolted to the jug and crankcase. A second problem is low mechanical stiffness and strength.
Another variable compression ratio engines having an adjustable distance between the cylinder head and crankshaft is taught by Howard C. Vivian in U.S. Pat. No. 4,174,683. The Vivian engine includes a crankcase or crankcase sub assembly (12), an upper cylinder head (10) and a cylinder block or cylinder jug (11). Cylinder block or cylinder jug (11) is connected to the crankcase (12) with a pair of eccentric shafts or control shafts (13 and 14). Vivian does not teach how to assemble eccentric control shafts (13 and 14) in cylinder jug (11) and crankcase (12) without having removable bearing caps, and Vivian does not teach how to provide a sturdy crankcase that is enclosed for containing engine oil within the crankcase.
Another variable compression ratio engines having an adjustable distance between the cylinder head and crankshaft is taught by Kodama of Toyota in U.S. Pat. No. 8,671,894. The Kodama engine includes a lower crankcase (22), an upper cylinder head (3) and a cylinder block or cylinder jug (2). Kodama does not teach how to provide a sturdy and compact variable compression ratio crankcase.
Another variable compression ratio engine having a pair of eccentric control shafts is taught by Werner Hoffrnann in US Publication Number US 2004/0035376 A1 of Feb. 26, 2004. Hoffman shows a cylinder jug (1) having eccentric control shafts (4) and removable bearing caps for securing eccentric control shafts (4) in crankcase (2). The eccentric control shafts are located near the top of the cylinder jug, and outboard of the water jacket. Locating the eccentric control shafts (4) near the top of the cylinder jug (1) results in a large spacing or bridging distance between the control shafts in order to clear the water jacket. The large bridging distance is undesirably large for providing a compact and rigid engine design. To minimize the bridging distance Hoffman uses undersized removable bearing caps for securing the eccentric control shafts (4) in the crankcase (1), where it can be seen (in FIG. 5) that the parting line surface of the bearing cap is too small and not mechanically sound.
Accordingly, an objective of the present invention is to provide a variable compression ratio engine having dual eccentric control shafts that is sturdy, rigid and compact. In more detail, an objective of the present invention is to provide a variable compression ratio mechanism having robust bearing housings for dual eccentric control shafts, closely spaced control shafts to provide a narrow engine with a small bridging distance between the eccentric control shafts to minimize structural bending and thermal distortion when the engine is running, and large enough control shafts and large enough control shaft bearings to support the high combustion loads of the engine. A narrow engine is also needed for fitting the engine into current production engine bays, where packaging an engine into an existing car model is exceptionally difficult. Another objective of the present invention is to provide a sealed crankcase for containing engine oil within the crankcase. Another objective is to provide an engine design that is inexpensive to manufacture and assemble.